1. Field of the Invention
The present invention relates to a fluid machine for a super charger for vehicles, for example.
2. Description of Relevant Art
There is disclosed in Japanese Utility Model Registration Publication No. 3-548 a compressor of such a root-type as 201 in FIGS. 1 and 2. In Japanese Patent Application Laid-Open Publication No. 61-182483, there is disclosed a compressor of a similar type, like 301 in FIG. 3.
The compressor 201 of FIG. 1 includes a compressor casing 203 and a pair of rotors 205 and 207. The rotors 205 and 207 rotate in opposite directions to each other in a rotor chamber 209 formed in the casing 203. Fluid suction and delivery ports 211 and 213 are provided through The casing 203, substantially at fight angles to an axial direction of the rotors 205 and 207.
As shown in FlG. 2, in the compressor 201 a convex part 217 is provided by forming steps 215 on each top of the rotors 205 and 207, and a sealed portion is defined among the convex part 217, a mating rotor, and the rotor chamber 209.
The sealed portion has raised fluid resistance as well as loss head between the rotors 205 and 207 and between the rotors 205, 207 and the rotor chamber 209, thereby decreasing leakage of fluid back to the suction port 211 side, improving a volumetric efficiency of the compressor 201.
In the compressor 301 of FIG. 3, the involute-type rotors 305, 307 have their teeth each configured in a form by circumferentially expanding a circular arcuate part at a top of an inherent narrow tooth, with an identical radius, to have an enlarged length for a sealing relative to an inner circumference 303a of a compressor casing, achieving an improved sealing property between suction side 309 and delivery side 311.
However, in the compressor 201 of FIG. 1, as will be seen from FIG. 2, the sealed portion has an insufficient length (along the convex part 217), and a resultant sealing property is limited in improvement.
In the compressor 301 of FIG. 3, the expanded form of the arcuate pan is engaged with a corresponding depression 305b, 307b of the mutually engaging rotors 305, 307, and the depression 305b, 307b needs to be cut wider so that a resultant configuration is reduced in thickness at the depression 305b, 307b, where it has a failed strength.